The bony chin and the associated musculature are recognized as an important source of lower face dysmorphology. Considerable attention in the maxillofacial and plastic surgery literature has been devoted to the diagnosis and treatment of chin deformity. The precision with which antero-posterior deformity and frontal asymmetry can be corrected has resulted in an increase in the demand for achieving technically precise bone cuts. However, the literature is sparse with regard to technical innovation to afford the surgeon a predictable, reproducible and precise chin osteotomy.
Chin recontouring surgery requires the placement of bones into new positions. If a symmetric movement of the chin is to be made in the antero-posterior plane, it is imperative that the osteotomy cuts be straight, of the same length and in the same plane. Otherwise, the movement of the inferior fragment to its new position will result in rotations of the fragment and gaps in the bone-to-bone contact. The result is asymmetry in the position of the chin point and inferior bone healing.
The traditional method of cutting bones in the face has been "freehand" (i.e. without a cutting guide), relying only on the care and technical capability of the surgeon for accuracy. "Freehand" cuts are very difficult to perform and can be rather imprecise, particularly where the cuts are made by two or more surgeons, which is often the case. To facilitate accurate and precise "freehand" surgery, the anterior surface of the mandible is exposed to a greater degree than it ought to be. Although this provides the surgeon with a better view of the entire surgical area to augment the accuracy of bone cutting, it also creates increased access to vital structures, such as the mental nerve or neurovascular bundle, that can be inadvertently damaged during the "freehand" cutting process. The inaccuracies of the "freehand" cutting methods lead to complications such as nerve damage, poor quality bone healing, bone resorption, less than symmetric placement of the chin, instability of the chin, increased operating time and increased blood loss. These significant disadvantages could be reduced or overcome with precise, quick and efficient bone cuts. It is therefore surprising that there has been no known cutting guide developed to perform chin recontouring surgery.
There are numerous prior art devices for precision cutting of bones in the appendicular skeleton, such as cutting guides for the replacement of the hip, knee and the shoulder. These include U.S. Pat. No. 5,049,149 (Schmidt) and U.S. Pat. No. 5,002,547 (Poggie et al.). Without exception, these prior art devices are designed for specific application to the long bones of the appendicular skeleton and are not suitable for cutting the axial skeleton, and in particular the chin, to aid in genioplasty. For example, most prior art guides must be clamped onto the bone being cut or must engage extensive surface areas on the bone for stability. In comparison, the chin is rather small with many vital structures in close proximity, hence it would be very difficult, if not impossible, to securely clamp a guide to the patient's chin or head as taught by the prior art.
What is desired therefore is a surgical cutting guide to be fixed to the anterior surface of the mandible having a guide surface to provide straight and accurate cuts of the mandible. The guide should also be capable of retracting vital elements of the chin to prevent damage thereto. Furthermore, it should reduce inter-operator error where two or more surgeons perform the cutting.